Microwave heating device

ABSTRACT

In a microwave heating apparatus, an electricity feeding port constituting a port of radiating a microwave is set to a ceiling wall of a heating chamber, a magnetron is arranged on a side of an outer side face of the heating chamber by directing an antenna for oscillating the microwave to a side of the heating chamber, and a wave guide for guiding the microwave oscillated from the magnetron to the electricity feeding port is formed in an L-like shape including a side wave guide extended upwardly from a surrounding of the antenna along the outer side face of the heating chamber and an upper wave guide extended from an upper end of the side wave guide to the electricity feeding port along an outer face of the ceiling wall.

TECHNICAL FIELD

The present invention relates to a microwave heating apparatus forheating a heating object such as food or the like by a microwave (highfrequency electromagnetic wave), particularly relates to an improvementin realizing small-sized formation of the apparatus by enabling toarrange a waveguide having a length in an axial direction equal to orlarger than a wavelength of a microwave in the waveguide at an upperportion of a heating chamber to thereby save a space thereof whilerestraining a deviation in an electric field intensity distributionbringing about an unevenness in heating.

BACKGROUND ART

A microwave heating apparatus of this kind is generally constituted toinclude a heating chamber containing an object to be heated, a magnetronfor oscillating a microwave, an electricity feeding port formed at awall face of the heating chamber from which the microwave is radiatedinto the heating chamber, a waveguide for guiding the microwave to theelectricity feeding port. A position of arranging the electricityfeeding port and a mode of the electricity feeding port are devised inorder to prevent an unevenness in heating from being brought about byreducing a deviation in an electric field intensity distribution atinside of the heating chamber.

As a position of arranging the electricity feeding port, any of innerwall faces partitioning the heating chamber is selectable andheretofore, there have been proposed various constitutions of aconstitution of providing the electricity feeding port at a side wall ofthe heating chamber, a constitution of providing the electricity feedingport at a bottom wall of the heating chamber, a constitution ofproviding the electricity feeding port at a ceiling wall of the heatingchamber and so on.

Further, generally, it is difficult to resolve the deviation in theelectric field intensity distribution at inside of the heating chamberby simply providing the electricity feeding port and in order to resolveoccurrence of the unevenness in heating caused by the deviation in theelectric intensity distribution, it is dispensable to mount rotatingmeans (stirrer) for stirring the microwave or a turntable for turningthe object at inside of the heating chamber and by mounting these, theapparatus tends to be large-sized.

In a market of the microwave heating apparatus in recent times,small-sized formation is required. Hence, there has been intensivelycarried out a research of achieving small-sized formation by omitting tomount the stirrer or the turntable by arranging the electricity feedingport at the ceiling wall of the heating chamber.

FIG. 7 shows a microwave heating apparatus of a background art arrangedwith an electricity feeding port constituting a port of radiating amicrowave at a ceiling wall of heating chamber (refer to, for example,JP-A-57-103292).

FIG. 7 is a sectional view viewing a microwave heating apparatus 1disclosed in JP-A-57-103292 as mentioned above, from a front side, andthe microwave heating apparatus 1 is constituted to include an externalcabinet 3, a heating chamber 5 for containing an object such as food orthe like to be heated, a magnetron 7 for oscillating a microwave, anelectricity feeding port 9 formed at a ceiling wall 11 of the heatingchamber 5 from which a microwave is radiated into the heating chamber 5,and a waveguide 13 for guiding the microwave oscillated from an antenna12 of the magnetron 7 to the electricity feeding port 9.

The magnetron 7 is arranged on a right outer side of the heating chamber5 and attached to a base end of the waveguide 13 in an attitude ofdirecting the antenna 12 upwardly.

The illustrated waveguide 13 is constituted by a shape of a straightpipe having a rectangular section and is provided with a length from asurrounding of the antenna 12 to the electricity feeding port 9.

Meanwhile, when a wave length of the microwave propagated at inside ofthe wave guide 13 is designated by notation λg, in order to efficientlyradiating the microwave from the electricity feeding port 9, with regardto a length in an axial direction of the wave guide 13, it is preferableto constitute a distance between the antenna 12 of the magnetron 7 and acenter of the electricity feeding port 9 by λg/2 multiplied by aninteger. Further, in order to restrain a deviation in an electric fieldintensity distribution bringing about a nonuniformity in heating, it ispreferable to make the electricity feeding port as proximate to a centerof the heating chamber as possible.

However, according to the wave guide 13 in the shape of the straightpipe as shown by FIG. 7, in the case in which a width dimension of theheating chamber 5 is designated by notation W₁, and a distance from aright side wall 15 of the heating chamber 5 to the center of theelectricity feeding port 9 is designated by notation L₁, when withregard to the length in the axial direction of the wave guide 13, thedistance between the antenna 12 and the center of the electricityfeeding port 9 is constituted by 3/2 λg, a clearance is produced betweenthe magnetron 7 and the right side wall 15.

The clearance becomes a wasteful space and therefore, although variousmethods have been adopted in order to prevent the wasteful space, first,when the magnetron 7 is shifted to a left side of the drawing, thedistance between the antenna 12 and the center of the electricityfeeding port 9 is shifted from λg/2 multiplied by an integer.

Second, when the magnetron 7 and the wave guide 13 and the electricityfeeding port 9 are simultaneously shifted to the left side of thedrawing, the electricity feeding port 9 is shifted from the center ofthe heating chamber 5.

Third, when the right side wall 15 of the heating chamber 5 is shiftedto a right side of the drawing, the electricity feeding port 9 issimilarly shifted from the center of the heating chamber 5.

Fourth, although it is conceivable to shift a left side wall of theheating chamber 5 to the left side simultaneous with the third method,in such a method, the width dimension W₁ of the heating chamber 5 isincreased.

Further, a height of the wave guide 13 needs to be equal to or largerthan a length of the antenna 12 and there also poses a problem that anincrease in a height dimension H₁ of the wave guide 13 gives rise to anincrease in the dimension in a height direction of the apparatus.

The invention has been carried out in view of the above-describedproblem and it is an object thereof to provide a microwave heatingapparatus capable of restraining a deviation in an electric fieldintensity distribution causing to bring about a nonuniformity in heatingby eliminating a wasteful space between a magnetron and an outer sideface of a heating chamber and setting an electricity feeding port at acenter in a width direction of the heating chamber even when a distancebetween an antenna and a center of the electricity feeding port is setto a half of a wave length of a microwave at inside of a wave guidemultiplied by an integer with regard to a length in an axial directionof the wave guide, capable of shortening a height dimension of theapparatus by contracting a height dimension of the wave guide along adirection of projecting an antenna of the magnetron and capable ofrealizing small-sized formation of the apparatus while restraining thenonuniformity in heating caused by a deviation in a position of mountingthe electricity feeding port from being brought about.

DISCLOSURE OF INVENTION

In order to achieve the above-described object, a microwave heatingapparatus according to the invention is characterized in a microwaveheating apparatus for radiating a microwave oscillated from a magnetronto a heating chamber via a wave guide, wherein an electricity feedingport constituting a port of radiating the microwave is provided at aceiling wall of the heating chamber, and the wave guide is formed in anL-like shape including a side wave guide extended upwardly along anouter side face of the heating chamber and an upper wave guide extendedfrom an upper end of the side wave guide to the electricity feeding portalong an outer face of the ceiling wall.

According to such a constitution, a distance between the antenna of themagnetron and a center of the electricity feeding port can easily bechanged by only changing a position of the magnetron and a length of theside wave guide in an up and down direction and therefore, even when awidth dimension of the heating chamber is any dimension, the distancecan be selected to be a half of a wave length in the wave guidemultiplied by an integer without including a wasteful space.

Further, in order to achieve the above-described object, the microwaveheating apparatus is characterized in that an antenna of the magnetronis arranged to be directed to a side of the heating chamber and to beopposed to the side wall and the side wall is formed with a bulgedportion bulged to an inner side of the chamber for avoiding interferencewith the antenna in the microwave heating apparatus.

According to the microwave heating apparatus constituted in this way, aheight dimension of the wave guide at the surrounding of the antenna ofthe magnetron is substantially constituted by adding a height dimensionh₃ of the bulged portion of the side wall of the heating chamber to anactual height dimension h₂ of the wave guide, the actual heightdimension h₂ per se of the wave guide can be shortened to a valuesmaller than a value of a length of projecting the antenna of themagnetron, thereby, a height dimension of the apparatus can be shortenedby contracting a dimension of the wave guide along the direction ofprojecting the antenna of the magnetron.

Further, small-sized formation of the heating chamber by the wave guidein the L-like shape and shortening of the height dimension of the waveguide by mounting the bulged portion to the side wall of the heatingchamber are synergetically combined and small-sized formation of theapparatus promoting space efficiency can be realized while preventingoccurrence of a nonuniformity in heating caused by a deviation of aposition of mounting the electricity feeding port.

Further, preferably, in the microwave heating apparatus, there may beconstructed a constitution in which the electricity feeding port isformed in a rectangular shape slender in a width direction of theheating chamber.

When constituted in this way, even by the electricity feeding portarranged at a position deviated from the center of the heating chamber,occurrence of the nonuniformity in heating can be restrained by reducinga deviation of an electric field intensity distribution at the heatingchamber.

Further, preferably, in the microwave heating apparatus, there may beconstructed a constitution in which a plurality of pieces of theelectricity feeding ports are provided.

Further, in that case, there may be constructed a constitution in whichthe plurality of electricity feeding ports are formed by at least two ormore kinds of electricity feeding ports having different shapes andopening areas.

Further, there may be constructed a constitution in which when theplurality of electricity feeding ports are aligned in a front and reardirection of the ceiling wall, the opening area of the electricityfeeding port at a position proximate to a center of the ceiling wall isset to be larger than the opening area of the electricity feeding portat a position remote from the center of the ceiling wall.

In this way, formation of the plurality of pieces of electricity feedingports and various formations of shapes and areas of the electricityfeeding ports are effective when the deviation of the electric fieldintensity distribution as a total of the heating chamber is alleviatedby adjusting rates of radiating the microwaves from the respectiveelectricity feeding ports when the position of mounting the electricityfeeding port is deviated from the center of the ceiling wall of theheating chamber.

Further, in the microwave heating apparatus, the microwave heatingapparatus is characterized in that a heating member in a linear shapefor heating by a heater is mounted to the ceiling wall of the heatingchamber and the electricity feeding port is mounted to a position atwhich a line equally dividing the ceiling wall into two in a front andrear direction is not included.

Further preferably, in the microwave heating apparatus, there may beconstructed a constitution in which a heating member in a linear shapefor heating by a heater is mounted to the ceiling wall of the heatingchamber and a center axis of the heating member is constituted to bemore proximate to a line equally dividing the ceiling wall into two in afront and rear direction than a center axis line in a width direction ofthe upper wave guide arranged at the ceiling wall.

When constituted in this way, adjustment for reducing a deviation in atemperature distribution of an atmosphere by radiating heat of theheating member can be carried out in correspondence with adjustment ofthe deviation of the electric field intensity distribution by themicrowave and occurrence of a nonuniformity in heating by the microwaveand the radiation heat can be reduced.

Further, in the microwave heating apparatus, there may be constructed aconstitution in which the heating member is arranged to be inclined tothe line equally dividing the ceiling wall into two in the front andrear direction.

When constituted in this way, in comparison with a case of arranging theheating member in parallel with the line equally dividing the ceilingwall of the heating chamber into two in the front and rear direction, aheating region of the heating chamber by the heating member is widenedin the front and rear direction of the heating chamber and thenonuniformity in heating by heating by a heater can further berestrained.

Further, in the microwave heating apparatus, there may be constructed aconstitution in which stirring means for stirring the microwave ismounted to a wall face of the heating chamber when space is permitted.

In this way, mounting of the stirring means is effective in furtherrestraining occurrence of the nonuniformity in heating by preventing thedeviation of the microwave in the heating chamber by stirring themicrowave.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of an inner portion or a first embodiment ofa microwave heating apparatus according to the invention in view from afront side thereof,

FIG. 2 is a view viewing FIG. 1 from an arrow mark of a line A-A,

FIG. 3 is a sectional view taken along a line B-B of FIG. 2,

FIG. 4 is a sectional view of an inner portion of a modified example ofthe first embodiment of the microwave heating apparatus according to theinvention viewed from the front side,

FIG. 5 shows an outline constitution of an inner portion of a secondembodiment of a microwave heating apparatus according to the inventionviewed from an upper side,

FIG. 6 illustrates explanatory views of other embodiment of anelectricity feeding port arranged at a front end of an upper wave guideaccording to the invention, and

FIG. 7 is a sectional view viewing a microwave heating apparatus of abackground art from a front side.

Further, in notations of the drawings, numeral 21 designates a microwaveheating apparatus, numeral 23 designates an object to be heated, numeral25 designates a heating chamber, notation 25 a designates a ceilingwall, notation 25 b designates a right side wall, numeral 27 designatesa magnetron, notation 27 a designates an antenna, numeral 29 designatesan electricity feeding port, notation 29 a designates an electricityfeeding port, notation 29 b designates an electricity feeding port,numeral 31 designates a wave guide, numeral 33 designates a heatingmember, numeral 35 designates a grill, numeral 37 designates anopening/closing door, numeral 41 designates a recessed portion, numeral43 designates a bulged portion, numeral 47 designates a side wave guide,numeral 49 designates an upper wave guide, and numeral 51 designates amicrowave heating apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

A detailed explanation will be given of a microwave heating apparatusaccording to a first embodiment of the invention in reference to theattached drawings as follows.

FIG. 1 through FIG. 3 show the first embodiment of the microwave heatingapparatus according to the invention, FIG. 1 is a sectional view of aninner portion viewed from the front side, FIG. 2 is a view viewing FIG.1 along an arrow mark of a line A-A, and FIG. 3 is a sectional viewtaken along a line B-B of FIG. 2.

The microwave heating apparatus 21 according to the first embodiment isprovided with the heating chamber 25 for containing the object 23 offood or the like, the magnetron 27 for oscillating a microwave, theelectricity feeding port 29 formed at a wall face of the heating chamber25 and constituting a port of radiating the microwave into the heatingchamber 25, the wave guide 31 for guiding the microwave oscillated fromthe magnetron 27 to the electricity feeding port 29, the heating member33 in a linear shape for heating by a heater, and a grill 35 mounted toa bottom portion of the heating chamber 25 for assisting heatingoperation.

Further, the above-described respective constituent elements includingthe heating chamber 25 are contained at inside of an external cabinet22.

The heating chamber 25 is formed in a shape of a box a front side ofwhich is made to be openable and closable by the opening/closing door37, as shown by FIG. 2 and FIG. 3, the heating member 33 is mounted toan upper portion of the heating chamber 25 frontward from a line X₁equally dividing the ceiling wall 25 a into two in a front and reardirection, further, the electricity feeding port 29 is mounted at aposition rearward from the line X₁ equally dividing the ceiling wall 25a into two in the front and rear direction.

A position of the ceiling wall 25 a in correspondence with the heatingmember 33 is formed with the recessed portion 41 for containing theheating member 33 and a consideration is given thereto such that theheating member 3 is not projected into the heating chamber.

In the case of the embodiment, the electricity feeding port 29 isconstituted by two of electricity feeding ports 29 a, 29 b positions ofwhich are shifted from each other in the front and rear direction.Either of shapes of the two electricity feeding ports 29 a, 29 b is arectangular shape slender in a width direction of the heating chamber 25(that is, in an axial direction of the wave guide 31, mentioned later).Further, the two electricity feeding ports 29 a, 29 b are provided at aregion which does not include a pipe axis Y₁ of the wave guide 31 (incorrespondence with an axial line constituting a center of a widthdimension a of the wave guide 31, mentioned later). Further, as shown byFIG. 2 and FIG. 3, an opening area of the electricity feeding port 29 aat a position proximate to a center of the ceiling wall 25 a is set tobe larger than an opening area of the electricity feeding port 29 b at aposition remote from the center of the ceiling wall 25 a.

The opening areas of the electricity feeding ports 29 a, 29 b are madeto differ from each other in this way for making a deviation of anelectric field intensity distribution as small as possible for an entireregion of inside of the heating chamber 25 by adjusting radiationefficiencies, radiation angles and the like of microwaves from therespective openings.

As shown by FIG. 1 and FIG. 2, the magnetron 27 is arranged on a side ofa right outer side face of the heating chamber 25 to direct the antenna27 a oscillating the microwave to a side of the heating chamber 25.

Further, the right side wall 25 b of the heating chamber 25 opposed tothe antenna 27 a is formed with the bulged portion 43 for avoidinginterference with the antenna 27 a in a mode of being bulged to an innerside of the chamber.

The wave guide 31 is formed in an L-like shape including the side guidewave 47 extended upwardly from a surrounding of the antenna 27 a alongthe right outer side face of the heating chamber 25 and the upper waveguide 49 extended from an upper end of the side wave guide 47 to theelectricity feeding port 29 along an outer face of the ceiling wall 25a.

The side wave guide 47 partitions a wave guide path in a shape of arectangular shape pipe for guiding the microwave in cooperation with theright side wall 25 b of the heating chamber 25. Further, the upper waveguide 49 partitions a wave guide path in a shape of a rectangular pipefor guiding the microwave in cooperation with the ceiling wall 25 a ofthe heating chamber 25.

In the case of the side guide wave 47, a height dimension h₂constituting a direction of projecting the antenna 27 a is set to besmaller than a length of projecting the antenna 27 a since interferencewith the antenna 27 a can be avoided by presence of a height dimensionh₃ of the bulged portion 43. A height dimension b of the upper waveguide 49 is set to be the same as the height dimension h₂ of the sidewave guide 47 (that is, b=h₂).

Further, a position of attaching the wave guide 31 to the heatingchamber 25 is set such that the electricity feeding port 29 a isdisposed on a front side of the apparatus and the electricity feedingport 29 b is disposed on a rear side of the apparatus interposing theaxis line Y₁ constituting the center of the width dimension a.

Such an attaching position effects influence on an electric fieldintensity distribution at inside of the heating chamber 25 and atemperature distribution of a heating atmosphere owing to a relationshipwith a wave length of the microwave radiated into the heating chamber25.

As shown by FIG. 3, when a separated distance to a center axis Y₂ of theheating member 33 from the line X₁ equally dividing the ceiling wall 25a into two in the front and rear direction is designated by notation p,and a separated distance to the center axis line Y₁ of the wave guide 31therefrom is designated by notation q, it is preferable to set arelationship of p<q and nullify p as much as possible.

Because although in the case of the microwave radiated from theelectricity feeding port 29 into the chamber 25, a radiation density atinside of the heating chamber 25 can be adjusted by various means of anopening area or an opening position of the electricity feeding port 29provided by the invention, or reflection by the grill 35 or the like andthe deviation of the electric field intensity distribution can easily beadjusted, with regard to a temperature distribution of an atmosphere byradiation by the heating member 33, in order to reduce a deviationthereof, it is best to install the heating member 33 per se as proximateto the center of the heating chamber 25 as possible.

According to the above-described constitution, as shown by FIG. 1, withregard to the length in the axial direction of the wave guide 31, evenwhen the distance between the antenna 27 a of the magnetron 27 and thecenter of the electricity feeding port 29 is set to, for example, 3/2 λgwhich is equal to a half of a wave length λg of the microwave in thewave guide multiplied by an integer by which the microwave canefficiently be radiated from the electricity feeding port 29, thedistance can easily be ensured by regarding the length in the axialdirection of the wave guide 31 as a sum of length dimensions Lλ1 +Lλ₂ ofthe upper wave guide 49 and the side wave guide 47 and adjusting theposition of the magnetron 27 and the length of the wave guide 47. As aresult, even when the width dimension of the heating chamber 25 isconstituted by any dimension, the electricity feeding port 29 can be setto the center of the heating chamber 25 and small-sized formation of theapparatus can be achieved by dispensing with formation of a wastefulspace between the magnetron 27 and the side wall 25 b of the heatingchamber 25 while preventing a nonuniformity in heating by a deviation ofan electric field intensity distribution from being brought about.

Further, according to the microwave heating apparatus 21 of theembodiment, a height dimension of the wave guide 31 at a surrounding ofthe antenna 27 a of the magnetron 27 is substantially constituted byadding the height dimension h₃ of the bulged portion 43 of the side wall25 b of the heating chamber 25 to the actual height dimension h₂ of thewave guide 31, the actual height dimension h₂ per se of the wave guide31 can be shortened to a value smaller than the length of projecting theantenna 27 a of the magnetron 27, thereby, the height dimension of theapparatus can be shorted by contracting the dimension of the wave guide31 along the direction of projecting the antenna 27 a of the magnetron27.

Further, small-sized formation of the heating chamber 25 by the waveguide 31 in the L-like shape and shortening of the height dimension ofthe wave guide 31 by mounting the bulged portion 43 to the side wall 25b of the heating chamber 25 are synergetically combined and small-sizedformation of the apparatus promoting space efficiency can be realizedwhile preventing a nonuniformity in heating caused by the deviation of aposition of mounting the electricity feeding port 29 from being broughtabout.

Further, the microwave heating apparatus 21 of the embodiment is mountedwith the heating member 33 and can be used also as an oven range (oventoaster) and therefore, the apparatus can be utilized for wider cookinguse.

Further, although the ceiling wall 25 a of the heating chamber 25 isprovided with both of the heating member 33 for heating by a heater andthe electricity feeding port 29 for heating by a microwave, the heatingmember 33 is made to be more proximate to the line X₁ equally dividingthe ceiling wall 25 a into two in the front and rear direction and theelectricity feeding port 29 and therefore, the deviation of thetemperature distribution of the atmosphere in the heating chamber 25 issmall and a drawback of the nonuniformity in heating or the like isdifficult to be brought about.

Meanwhile, the electricity feeding port 29 is disposed at the center ofthe width direction of the heating chamber 25 and is arranged to bedeviated rearward from the center of the heating chamber 25 only in thefront and rear direction of the heating chamber 25. Hence, with regardto such an eccentricity in the front and rear direction, the electricityfeeding port 29 a having a large aperture and the electricity feedingport 29 b having a small aperture are combined to thereby make radiationof the microwave into the heating chamber 25 as uniform as possible, asa result, even in the case of the microwave heating, the deviation inthe electric field intensity distribution at inside of the heatingchamber 25 is restrained to thereby restrain occurrence of thenonuniformity in heating, even when mounting of a turn table or the likewhich gives rise to large-sized formation of the apparatus is omitted,uniform heating to the object can be realized and small-sized formationof the apparatus can be realized without sacrificing the heatingcharacteristic.

FIG. 4 shows a modified example of the microwave heating apparatusaccording to the first embodiment of the invention.

According to the modified example, the wave guide 31 formed in theL-like shape by including the side wave guide 47 and the upper waveguide 49 is constituted such that the side wave guide 47 is formed toextend to a lower side of the heating chamber 25 and the magnetron 27 isarranged at a position below the heating chamber 25. Further, the otherconstitution is the same as that of the first embodiment.

By arranging the magnetron 27 at the position below the heating chamber25 in this way, small-sized formation can further be achieved byshortening the width dimension of the apparatus.

FIG. 5 shows an outline constitution of an inner portion of a secondembodiment of a microwave heating apparatus according to the inventionviewed from an upper side.

According to a microwave heating apparatus 51 of the second embodiment,the heating member 33 for heating by a heater is arranged to be inclinedto the line X₁ equally dividing the ceiling wall 25 a into two in thefront and rear direction and the other constitution is common to thecase of the first embodiment. Constitutions common to those of the firstembodiment are attached to the same notations and an explanation thereofwill be omitted.

When constituted in this way, in comparison with the case of the firstembodiment in which the heating member 33 is arranged in parallel withthe line X1 equally dividing the ceiling wall 25 a into two in the frontand rear direction, a heating region of the heating chamber 25 iswidened in the front and rear direction and a nonuniformity in heatingby an oven can further be restrained.

Further, in the microwave heating apparatus according to the invention,it is preferable to set a width dimension a and a height dimension b ofthe wave guide having a rectangular section shown in FIG. 6( a) tosatisfy Equation (1) and Equation (2) as follows when the wave length ofthe microwave in a free space is designated by notation λ₀.(λ₀/2)<a<λ ₀   (1)b<(λ₀/2)   (2)

Further, although according to the above-described respectiveembodiments, two pieces of the main and sub electricity feeding portsare arranged to align in the front and rear direction, a number ofmounting the electricity feeding ports is not limited to that of theabove-described embodiments. The number of mounting the electricityfeeding port can also be made to be single and can also be set to aplurality of pieces of 3 pieces or more.

Further, design of the electricity feeding port such as mountingposition, shape, opening area or the like can pertinently be changed inaccordance with a degree of being proximate to the line X₁ equallydividing the ceiling wall 25 a of the heating chamber 25 into two in thefront and rear direction.

In sum, the electricity feeding port may be made to be able to adjustsuch that the deviation of the electric field intensity distributioncausing the nonuiformity in heating is eliminated as much as possible.

FIGS. 6( b) through 6(f) show modified examples of the mounting positionand the mounting number of the electricity feeding port 29 at the frontend of the upper wave guide 49. In this way, the electricity feedingport can be designed variously.

FIG. 6( b) shows an example of mounting the single electricity feedingport 29 slender in the axial direction by aligning the center to thecenter axis line Y₁ in the width direction of the upper wave guide 49.

FIG. 6( c) shows an example of mounting the single electricity feedingport 29 slender in the axial direction by being shifted to the frontside from the center axis line Y₁ in the width direction of the upperwave guide 49.

FIG. 6( d) shows an example of mounting the single electricity feedingport 29 slender in the axial direction by being shifted considerably tothe front side not to be caught by the center axis line Y₁ in the widthdirection of the upper wave guide 49.

FIG. 6( e) shows an example of mounting the two electricity feedingports 29, 29 slender in the axial direction respectively to the frontside and the rear side interposing the center axis line Y₁ in the widthdirection of the upper wave guide 49.

FIG. 6( f) shows an example of mounting the electricity feeding portslender in the axial line direction frontward from the axis line Y₁ notto be caught by the center axis line Y₁ in the width direction of theupper wave guide 49 and mounting an electricity feeding port 30 slenderin a direction orthogonal to the axis line Y₁ to be partially caught bythe axis line Y₁.

There is also conceivable a structure of mounting a number ofelectricity feeding ports in a shape of a matrix in an axial directionalthough not illustrated. Further, there is also conceivable that aplurality of mounted electricity feeding ports are formed by electricityfeeding ports of at least two or more kinds having different shapes andopening areas. For example, an electricity feeding port may beconstituted by a circle, an ellipse, a triangle or other polygonal shapeor may be formed only by a curve or a curve and a straight line.

The above-described formation of a plurality of pieces of theelectricity feeding ports, various formations of shapes and areas of theelectricity feeding ports or the like are effective in alleviating thedeviation of the electric field intensity distribution as a total of theheating chamber 25 by adjusting a rate of radiating the microwave fromeach electricity feeding port 29 when the mounting position of theelectricity feeding port 29 is deviated from the center of the ceilingwall 25 a of the heating chamber 25.

Further, although in FIG. 6, there is a clearance between theelectricity feeding port and a left end portion of the wave guide, theremay be constructed a constitution of dispensing with the clearance.

Further, stirring means for stirring the microwave may be mounted to theinner wall face of the heating chamber when there is allowance indimensions and the like although the stirring means is not mounted inthe above-described embodiments since small-sized formation is made tobe mostly predominant.

Mounting of the stirring means is effective in restraining occurrence ofthe nonuniformity in heating by preventing the deviation of themicrowave by stirring the microwave.

Although an explanation has been given of the invention in details andin reference to the specific embodiments, it is apparent for the skilledperson that the present invention can variously be changed and modifiedwithout deviating from the sprit and the range of the invention.

The application is based on Japanese Patent Application No. 2003-028450filed on Feb. 5, 2003 and a content thereof is incorporated here byreference.

INDUSTRIAL APPLICABILITY

According to the microwave heating apparatus of the invention, bysetting the length in the axial direction of the wave guide as the sumof the length dimensions on the upper wave guide and the side waveguide, even when the width dimension of the heating chamber is anydimension, the electricity feeding port can arbitrary be set andoccurrence of the nonuniformity in heating by the deviation of theelectric field intensity distribution can be prevented. Further,small-sized formation of the apparatus can be achieved by eliminatingformation of a wasteful space between the magnetron and the side wall ofthe heating chamber.

Further, when the invention is constructed by a constitution describedin claim 2, the height dimension of the wave guide at the surroundingthe antenna of the magnetron is substantially constituted by adding theheight dimension h₃ of the bulged portion of the side wall of theheating chamber to the actual height dimension h₂ of the wave guide, theactual height dimension h₂ of the wave guide per se can be shortened tothe value smaller than the length of projecting the antenna of themagnetron, thereby, the height dimension of the apparatus can beshortened by contracting the dimension of the wave guide along thedirection of projecting the antenna of the magnetron.

Further, small-sized formation of the heating chamber by the wave guidein the L-like shape and shortening of the height dimension of the waveguide by mounting the bulged portion to the side wall of the heatingchamber are synergetically combined and small-sized formation of theapparatus promoting space efficiency can be realized while preventingoccurrence of the nonuniformity in heating caused by the deviation ofthe position of mounting the electricity feeding port.

1. A microwave heating apparatus for radiating a microwave oscillatedfrom a magnetron to a heating chamber via a waveguide, wherein aplurality of electricity feeding ports for radiating the microwave areprovided at a ceiling wall of the heating chamber, and the wave guide isformed in an L-like shape including a side waveguide extended upwardlyalong an outer side face of the heating chamber such that the sidewaveguide is in direct contact with the outer side face of the heatingchamber and an upper waveguide extended from an upper end of the sidewave guide along an outer face of the ceiling wall to an end portionopposed to the upper end of the side waveguide, wherein the upperwaveguide has opposing front and rear waveguide walls extended from theupper end of the side waveguide to the end portion of the upperwaveguide, wherein the plurality of electricity feeding ports are formedby at least two or more kinds of electricity feeding ports havingdifferent shapes and opening areas, wherein when the plurality ofelectricity feeding ports are aligned in a front and rear direction ofthe ceiling wall, the opening area of the electricity feeding port at aposition proximate to a center of the ceiling wall is set to be largerthan the opening area of the electricity feeding port at a positionremote from the center of the ceiling wall, and the opening area of theelectricity feeding port at a position proximate to the center of theceiling wall reaches the end portion of the upper waveguide and a cornerof the upper waveguide, and the opening area of the electricity feedingport at a position remote from the center of the ceiling wall reachesthe end portion of the upper waveguide and does not reach the rearwaveguide wall, wherein a distance between an antenna of the magnetronand a center of the opening area of each of the electricity feeding portat a position proximate to the center of the ceiling wall and theelectricity feeding port at a position remote from the center of theceiling wall is g/2 multiplied by an integer, wherein g is a wavelengthof the microwave propagated at an inside of the waveguides, and whereinan inclined face is formed at a connecting portion between the upperwaveguide and the side waveguide.
 2. The microwave heating apparatusaccording to claim 1, wherein the antenna of the magnetron is arrangedto be directed to a side of the heating chamber and to be opposed to theside wall and the side wall is formed with a bulged portion bulged to aninner side of the chamber for avoiding interference with the antenna. 3.The microwave heating apparatus according to claim 1, wherein theplurality of electricity feeding ports are formed in a rectangular shapeslender in a width direction of the heating chamber.
 4. The microwaveheating apparatus according to claim 1, wherein a heating member in alinear shape for heating by a heater is attached to the ceiling wall ofthe heating chamber and a center axis of the heating member isconstituted to be more proximate to a line equally dividing the ceilingwall into two in a front and rear direction than a center axis line in awidth direction of the upper wave guide arranged at the ceiling wall. 5.The microwave heating apparatus according to claim 4, wherein theheating member is arranged to be inclined to the line equally dividingthe ceiling wall into two in the front and rear direction.
 6. Themicrowave heating apparatus according to claim 1, wherein the heatingmember is positioned such that a horizontal centerline of the heatingmember is located above the opening areas of the plurality of feedingports.
 7. The microwave heating apparatus according to claim 1, whereinthe magnetron is disposed adjacent to the side surface at the lateralside of the heating chamber and adjacent an end of the side wave guidethat is extended away from the upper wave guide.
 8. The microwaveheating apparatus according to claim 1, wherein a heating member in alinear shape for heating by a heater is mounted in a recessed portion ofthe ceiling wall of the heating chamber and the plurality of electricityfeeding ports are mounted to the ceiling wall, both the heating memberand the plurality of electricity feeding ports being mounted at aposition away from a line equally dividing the ceiling wall into two ina front and rear direction.
 9. A microwave heating apparatus forradiating a microwave oscillated from a magnetron to a heating chambervia a waveguide, wherein a plurality of electricity feeding ports forradiating the microwave are provided at a ceiling wall of the heatingchamber, and the wave guide is formed in an L-like shape including aside waveguide extended upwardly along an outer side face of the heatingchamber and an upper waveguide extended from an upper end of the sidewave guide ports along an outer face of the ceiling wall to an endportion opposed to the upper end of the side waveguide, wherein theupper waveguide has opposing front and rear waveguide walls extendedfrom the upper end of the side waveguide to the end portion of the upperwaveguide, wherein the plurality of electricity feeding ports are formedby at least two or more kinds of electricity feeding ports havingdifferent shapes and opening areas, wherein when the plurality ofelectricity feeding ports are aligned in a front and rear direction ofthe ceiling wall, the opening area of the electricity feeding port at aposition proximate to a center of the ceiling wall is set to be largerthan the opening area of the electricity feeding port at a positionremote from the center of the ceiling wall, and the opening area of theelectricity feeding port at a position proximate to the center of theceiling wall reaches the end portion of the upper waveguide and a cornerof the upper waveguide, and the opening area of the electricity feedingport at a position remote from the center of the ceiling wall reachesthe end portion of the upper waveguide and does not reach the rearwaveguide wall, wherein a distance between an antenna of the magnetronand a center of the opening area of each of the electricity feeding portat a position proximate to the center of the ceiling wall and theelectricity feeding port at a position remote from the center of theceiling wall is g/2 multiplied by an integer, wherein g is a wavelengthof the microwave propagated at an inside of the waveguides, and whereinan inclined face is formed at a connecting portion between the upperwaveguide and the side waveguide.
 10. The microwave heating apparatusaccording to claim 9, wherein the magnetron is disposed adjacent to theside surface at the lateral side of the heating chamber and adjacent anend of the side wave guide that is extended away from the upper waveguide.
 11. The microwave heating apparatus of claim 9 wherein a width ofthe waveguide is greater than λ₀/2 and less than λ₀ and the height ofthe waveguide is less than λ₀/2, wherein λ₀ is a wavelength of themicrowave in a free space.